Shooting on a prime lens offers some technical benefits but I believe the creative benefits to be most important. Put simply I feel that restrictions foster creativity. When I don't know what to go out and photograph I try to give myself a particular assignment. Such as, capture bicycles or interesting plays of light. Using a prime lens is just as much of a limitation but opposed to subject matter it is a technical limitation. So, rather than changing what is being shot, a prime lens changes how you shoot. To be explicit, a prime lens is a fixed focal length (I shoot on a 40mm prime). As such, going out with a prime is also a creative limitation and forces you to think about the characteristics of that focal length.